This application relates generally to imaging. More specifically, this application relates to imaging objects or scenes electromagnetically using radiation with frequencies outside the visual spectrum.
Many methods of acquiring information about objects and/or scenes rely on the same fundamental process: the object or scene is irradiated and the response of the object or scene to the radiation is detected. This may be performed using a variety of different types of radiation, including the very familiar electromagnetic and acoustic radiation, as well as less common forms of radiation such as electron-beam, neutron beam, proton-beam, pion-beam, and other types of radiation. In addition to the ability to use these different types of radiation to extract information about objects, it is possible to detect different response when the energy of the radiation is changed.
Electromagnetic and acoustic radiation are especially familiar because they are the two forms of radiation that are most relied on by human beings in acquiring information about objects in the form of vision and hearing. The human sense of vision represents nothing more than the use of the human eye and related neurological structure as an electromagnetic detector that is sensitive to certain wavelengths of light. When an object is illuminated by light, it reflects the light in ways that the human eye can detect to provide information that the human brain may use to ascertain the type of material of the object, its shape, its texture, and so on. Human hearing functions in the same way, with the ear and related neurological structure acting as an acoustic detector sensitive to certain wavelengths of sound. When an object is irradiated by sound, the object reflects the sound in ways that the human ear can used to provide information usable by the human brain for similar kinds of analyses.
One limitation to both human vision and hearing is that the detection range provided by the human eye and ear are relatively narrow. Many objects respond to electromagnetic and/or acoustic radiation at wavelengths that are outside the ability of human senses to detect. For example, it is well known that only certain human tissue is transparent at x-ray wavelengths while other tissue is opaque, causing x-ray illumination to be a very widely used diagnostic tool. Similarly, the use of ultrasonic acoustic waves permits diagnostic information to be acquired that is not directly possible using human senses.
But while it is possible to cause objects to generate a response using radiation outside the detection range of human senses, that response must often still ultimately be evaluated by human beings who remain limited by their biological sensory range. This is true, for instance, in cases where the information is used in medical diagnostics and treatment. For example, the use of x-rays and ultrasound can provide information to a physician about the presence of a malignancy, but only when the information is converted into a form that can be understood by the physician. This is most commonly done by rendering an image in the visual spectrum that corresponds to the object and presenting this image on a planar surface, such as on a screen or a piece of paper. The image is then viewed independently of the original object and inferences are made about the original object.
This general approach has had much success in providing such things as x-ray images that may be viewed by physicians before they begin surgeries, and the like. But the approach is inherently limited by divorcing the generated image from the object being imaged in space and in time. There is accordingly a need in the art for improved methods of imaging objects using radiation outside the range of direct human detection.